I couldn’t put a number on it, but I feel I spent the most time in Act 3 in my ~85 hour playthrough of the game.
Granted, I mostly just slaughtered my way through the forge, the Cresh, and most of Act 2, so I certainly missed a fair bit of story content.
Act 3 is pretty packed with content, but at a certain point I became very comfortable with the idea of just not doing everything and enjoyed ending the game much more for it.
I don’t understand you completionists. The way y’all play games sounds inevitably exhausting to me. XD